The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hydraulic fracturing is a primary tool for improving well productivity by placing or extending high-permeability flow passages from the wellbore to the reservoir. This operation is essentially performed by hydraulically injecting a fracturing fluid into a wellbore penetrating a subterranean formation and forcing the fracturing fluid against the formation strata by pressure. The formation strata or rock is forced to crack and fracture. Proppant is placed in the fracture to prevent the fracture from closing and thus, provides improved flow of the recoverable fluid, i.e., oil, gas or water.
The success of a hydraulic fracturing treatment is related to the fracture conductivity, which is the ability of fluids to flow from the formation through the proppant pack. In other words, the proppant pack or matrix must have a high permeability relative to the formation for fluid to flow with low resistance to the wellbore.
In traditional fracturing operations, techniques have been used to increase the permeability of the proppant pack by increasing the porosity of the interstitial channels between adjacent proppant particles within the proppant matrix. These traditional operations seek to distribute the porosity and interstitial flow passages as uniformly as possible in the consolidated proppant matrix filling the fracture, and thus employ homogeneous proppant placement procedures to substantially uniformly distribute the proppant and non-proppant, porosity-inducing materials within the fracture.
A recent approach to improving hydraulic fracture conductivity has been to try to construct proppant clusters in the fracture, as opposed to constructing a continuous proppant pack. U.S. Pat. No. 6,776,235 (England) discloses a method for hydraulically fracturing a subterranean formation involving alternating stages of proppant-containing hydraulic fracturing fluids contrasting in their proppant-settling rates to form proppant clusters as pillars that prevent fracture closing. This method can, for example, alternate the stages of proppant-laden and proppant-free fracturing fluids to create proppant clusters in the fracture and open channels between them for formation fluids to flow. Thus, the fracturing treatments result in a heterogeneous proppant placement (HPP) and a ‘room-and-pillar’ configuration in the fracture, rather than a homogeneous proppant placement and consolidated proppant pack. The amount of proppant deposited in the fracture during each HPP stage is modulated by varying the fluid transport characteristics (such as viscosity and elasticity), the proppant densities, diameters, and concentrations and the fracturing fluid injection rate.
Proppant placement techniques based on the fracture geometry have been developed for use during traditional proppant pack operations. However, proppant placement in HPP is considerably more challenging and the art is still in search of ways to improve the proppant placement techniques in HPP operations. In practice, a predetermined proppant pumping schedule was followed presuming the desired fracture geometry would result. There is a need in the art of HPP operations for real-time evaluation of the actual fracture geometry and, if needed, a way to modify or adjust a proppant placement schedule to improve the ultimate fracture geometry.